1. Field
The present invention relates to methods and apparatus for monitoring and controlling the properties of fluids, and more particularly to a method and apparatus for quality control of fluids during manufacturing processes.
2. Description of Related Art
When manufacturing lubricating fluids blended with additives, analytical testing is required to verify that the properties of the blended lubricant are within defined specifications. The blending operation, in some exemplary approaches, may be performed in a tank or by in-line blending processes. Typical analytical tests, such as Fourier Transform Infrared (FT-IR) spectroscopy, kinematic viscosity as per ASTM D-445 or metal analyses—inductively coupled plasma spectrometry (ICP) as per ASTM D-5185, are performed on samples in a laboratory. Depending on laboratory operations and conditions, tests may require more than an hour for completion, and the blending process is typically suspended until satisfactory results are obtained. The delays may be extended if the results are unsatisfactory.
Systems for in-situ (e.g., performed in an operating system, such as an engine or transmission) monitoring of lubricating fluids are known. One such system is disclosed in U.S. Pat. No. 6,278,281 entitled “Fluid Control Monitor” issued to Bauer, et al. This patent describes a technique employing AC electro-impedance spectroscopy (referred to hereinafter as impedance spectroscopy or “IS”), and is implemented by means of probe electrodes placed in contact with the fluid to be tested. The method of operation includes making IS measurements at a first frequency that is less than 1 Hz and a second frequency that is greater than 1 Hz, comparing the two IS measurements, and declaring a “pass” or “fail” condition based on a previously determined empirical relationship.
However, this prior art lubricating fluid monitoring system effectively analyzes only a single characteristic of the IS spectra based on the difference of two IS measurements. Consequently, it is not capable of determining the complex properties of compound fluids, as is required when performing quality control measurements of fluids having a plurality of additives. Thus, a need exists for a real-time, in situ monitoring system for quality control of fluids during manufacturing operations.